EEVblog #1110 - Mailbag

[EEVblog]

More than an hour of Mailbag!


SPOILERS:
Sony DVO-1000MD medical device video DVD recorder teardown
8:09 Security ISA card teardown from the 1980's
18:39 Power Grid the board game!
25:02 USB soldering iron
27:21 TI-nSpire CAS+ calculator PROTOTYPE!
35:28 DIY JBC/Hakko soldering iron controller
https://www.team-ncrc.com/shop/product/soldering-station-jbc?utm_source=eevblog&utm_medium=mailbag
41:49 UV LED lamp for PCB exposure
45:10 DIY battery spot welder
https://www.keenlab.de/index.php/portfolio-item/kweld/
51:44 10W Laser Diode circuit PCB design review
https://www.kickstarter.com/projects/stac/stac-researching-the-impact-of-life-in-space
1:00:00 EL light teardown
1:02:41 IC2 rotary encoder Kickstarter
https://www.kickstarter.com/projects/1351830006/i2c-encoder-v2

[ataradov]

That security thing appears to be super easy to bypass. Just drill tiny  holes (< width of the track) and use thin wire to short the posts, then dremel all you want.

[sleemanj]

I keep one of those around for emergency purposes, handy for if I need to fix something on a vehicle, or to fix the proper soldering iron...

[free_electron]

Those powerso packages don't need equalisation resistors. Simply mount them close together and link them thermally. the resistance in the solder joints and copper on the board does the rest.
Some of these transistors are in the 1 to 2 milliohms when 'on'. I have made couple of boards where they switch 200 ampere without even blinking.

[alxpo]

This ground trace for current sensing resistor on the laser PSU board is absolutely useless because connected to the ground plane on both ends.

[TurboTom]

Paralleling MOSFETs that are supposed to work in analog (controlled resistance) mode dosn't work as simple as done on that laser controller board, neither the small source resistors that Dave mentioned will work.
Actually, the way to go is to have a separate current sense amp for every individual transistor, driving its gate. If the threshold voltage of the individual FETs differs only slightly, one will end up with the transistorwith the lowest threshold taking almost all of the "punishment" while the others are virtually still blocked. For paralleling bipolar transistors, the distributed emitter resistance will work but then they are current and not voltage driven. Moreover, when using modern MOSFETs in analog high current/high dissipation mode, one has to make sure that the SOA of the device permits that kind of operation at all. Typical electronic load passbanks show how to do it.
Dave's note regarding ground referencing of the sense amps is also a little misleading, though he probably meant the correct thing: It's not important to reference the negative power supply rail of the sens amps closely to the current shunt negatives but rather the reference of the input signal to the current sense amps, i.e. the ground of the D/A converter or whatever means is used to set the current.
According to the circuitry, the laser doesn't appear to be operated in fast pulse mode. Considering this, it may be necessary to revice the thermal design of the passbank, especially if it's supposed to be operated in vacuum.

All the best with the project!


Cheers,
Thomas

[tautech]

45:10 DIY battery spot welder

All started here:
https://www.eevblog.com/forum/projects/guesses-on-what-i-am-attempting-here/

[Urs42]

I've sent you the ISA security Card, it is from an old ATM, i do not have any more information about it  Our note is written with the UV marker, you can use the included UV light to read it...

You can dissolve the outer layers of the smartcard with acetone. We did that with a second broken card i have.

[screwbreaker]

For the DVD 99% is just the belt. Clean it, grease a little if needed and replace the belt.

[free_electron]

Paralleling MOSFETs that are supposed to work in analog (controlled resistance) mode dosn't work as simple as done on that laser controller board, neither the small source resistors that Dave mentioned will work.
Actually, the way to go is to have a separate current sense amp for every individual transistor, driving its gate. If the threshold voltage of the individual FETs differs only slightly, one will end up with the transistorwith the lowest threshold taking almost all of the "punishment" while the others are virtually still blocked. For paralleling bipolar transistors, the distributed emitter resistance will work but then they are current and not voltage driven. Moreover, when using modern MOSFETs in analog high current/high dissipation mode, one has to make sure that the SOA of the device permits that kind of operation at all. Typical electronic load passbanks show how to do it.
Dave's note regarding ground referencing of the sense amps is also a little misleading, though he probably meant the correct thing: It's not important to reference the negative power supply rail of the sens amps closely to the current shunt negatives but rather the reference of the input signal to the current sense amps, i.e. the ground of the D/A converter or whatever means is used to set the current.
According to the circuitry, the laser doesn't appear to be operated in fast pulse mode. Considering this, it may be necessary to revice the thermal design of the passbank, especially if it's supposed to be operated in vacuum.

All the best with the project!


Cheers,
Thomas

That's what they do in the agilent 6060 programmable load. one sense amp per transistor , 10 banks in parallel. so each transistor takes its share of the load.

These power-so packages are not made for use in linear domain. They can't dissipate anything. it is always hard on or completely off. ( static switching , not even pwm)
For that purpose you can simply put them parallel.

On semiconductor FDMT80040 handles 400 ampere without blinking...  RDSon is 0.56 milliohms. That is in the order of the solderjoint resistance... for these small landpads the solder resistance is in the range of 0.2 to 0.25 milliohms. Fortunately there is a big bulk pad to lower this substantially on the drain but the source remains problematic. the three pins parallel are still in the order of 0.05 to 0.1 milliohm.

The top pad is used for cooling using a heatsink.

[SeanB]

ISA card is used in an ATM to decode the PIN off the track 2 data from the card. The PIN is encoded on the magstripe, and the keyboard entered PIN is used via the onboard processor in the card (80C186 processor in a minimal configuration) to give a pass/fail result for the PIN entry when used in offline mode, and encrypts the PIN and account number, plus the requested value and a nonce, for transmission up the line to the payment processor, as the banks consider the line link a non secure channel. The secure processor is there as the only secret in the ATM, containing data specific to the payment processor who supplies the ATM link, the bank and a machine specific serial number, all of which are used to uniquely identify the ATM, the transaction and allows the machine to be used outside the bank teller network securely.

[rsjsouza]

I keep one of those around for emergency purposes, handy for if I need to fix something on a vehicle, or to fix the proper soldering iron...

I have a Weller AA-powered soldering iron, and it works well for leaded solder and emergencies.

Regarding the ISA card. Just like Dave, I find it quite strange the ISA card does not have a battery inside its security chamber (the board looks too old and leakage would be too high for a supercap). I worked in some designs where a much denser ratsnest was tied to a dormant low leakage micro (MSP430F110 at the time) and a CR2032 would have an endurance much larger than the battery itself.

[langwadt]

Those powerso packages don't need equalisation resistors. Simply mount them close together and link them thermally. the resistance in the solder joints and copper on the board does the rest.
Some of these transistors are in the 1 to 2 milliohms when 'on'. I have made couple of boards where they switch 200 ampere without even blinking.

which is fine for switching but not for linear mode, though looking at SOA for those FETs are pretty much useless for linear mode anyway

[Bud]

. The PIN is encoded on the magstripe

No it is not. PIN is _derived_ from the magstripe data elements. It would be crazy to put the PIN on the mag which anyone can read.

[asgard]

Did the student group post a link to an Eagle file or PDF schematic?  I did not see anything on their kickstarter page.  I'd like to study the same things mentioned about the layout but it whizzes by pretty rapidly on the video.

[Poe]

FYI
The image in Dave's video regarding FETs in parallel and an explanation comes from:
https://www.nxp.com/docs/en/user-guide/MOSFET-Application-Handbook.pdf
Page 183

[Kleinstein]

I keep one of those around for emergency purposes, handy for if I need to fix something on a vehicle, or to fix the proper soldering iron...

I have a Weller AA-powered soldering iron, and it works well for leaded solder and emergencies.

Regarding the ISA card. Just like Dave, I find it quite strange the ISA card does not have a battery inside its security chamber (the board looks too old and leakage would be too high for a supercap). I worked in some designs where a much denser ratsnest was tied to a dormant low leakage micro (MSP430F110 at the time) and a CR2032 would have an endurance much larger than the battery itself.

I am not surprised to not find the battery inside the sealed / secure part. The battery might need replacement at some time and there is no real need to have the battery inside. It is only used for backup and thus should not have a signal dependent current anyway. The way the integrity is checked is a little off. At least with knowing the inner construction it would be relatively easy to fool  it.

I have sometimes used a small battery powered soldering iron. Not very powerful, but OK for normal small parts, but it was very fast (e.g. some 2 or 3 seconds)  to heat up and this way very convenient.  However the shown tip looks odd: rather large part to get hot.

[Quarlo Klobrigney]

Confessions of an Atmel fanboy here.... The 2313 is my favorite back in the day.
Firstly I don't see any bypass caps on the IC's on that laser board, i.e. 100nF.
Also there is no cap on the reset pin, usually a 10nF with a 10K pullup.
That reset line must come up slowly, not just a pullup. Read the datasheet.

As far as the missing legends, if it's an Eagle design, the libraries are at fault. Most rookies forget to place the >NAME on the tNames and the >VALUE on the tValues layers.

Yes the Maxim unobtanium. I remember back in the 90's contacting a distributor here in Florida. He said he would leave a "few" books for me outside the office door.
They totaled about a foot tall. I drooled over the possibilities of the chips and thought of all sorts of projects to make.
Only to find out.....No chips available.

[bigsky]

Just a couple of thoughts on the secure ISA card:

The WD2001-PH chip is a "data encryption device" - see http://www.leadelectronics.com/product-details.php?item_no=WD2001PH-20-02&manu_no=WEDI&catid=135

It has a 15 pin D connector, which in days gone by was found on ethernet cards - see https://en.wikipedia.org/wiki/Attachment_Unit_Interface

So I reckon it might be a secure ethernet card. I don't know about ATMs, but these were definitely used in the financial industry (stock exchange networks for share trading, possibly other banking applications) where very high levels of security were needed.

[f4eru]

You can dissolve the outer layers of the smartcard with acetone

The acetone needs an hour, plus some scratching action.
That LCD is a flexible LCD. Amazing tech.

[CChin254]

Here is the IC Identification of the Texas Instruments TI-Nspire CAS+ (Prototype). Instead of uploading it as individual photos, I now upload them as a whole PDF that you can download.